can't use an undefined value as a symbol perl

问题

I'm trying to write in file some value taken from an array. But I'm having some error ''Can't use an undefined variables as a symbol reference at... line 81:

foreach $k (sort keys %{$value2}){
    print $value4 $k." = ".%{$value2{$k}}. $value3;



sub printit{
  $value1 = $_[0];#"ipadress" is a string
  $value2 = $_[1];#%hash2
  $value3 = $_[3];#"paquet" is a string
  $value4 = $_[4];#SOURCE is the file name

  foreach $k (sort keys %{$value2}){
    print $value4 $k." = ".%{$value2{$k}}. $value3;
    if (%{$value2{$k}} >= 2) { print $value4 "s";}
    print $value4 "\n";
  }
}

printit('ipadress', \%hash2, ' paquet'. SOURCE );

Could someone please indicate me what's wrong?

the things is my code is this one and it work fine. And I didn't concatanate SOURCE and it's still working fine.

print SOURCE "Ipadress #2\n\n";
foreach $k (sort keys %hash2){
  print SOURCE $k." = ".$hash2{$k}." paquet";
  if ($hash2{$k} >= 2) { print SOURCE "s";}
  print SOURCE "\n";
}

but I'm having a lot of codes that does the same thing so I wanted to create a function to be able reduce the numbers of lines.

回答1:

Your forgot a comma or concatenation here:

print $value4 $k." = ".%{$value2{$k}}. $value3;

Perl thinks you want to use $value4 has a filehandle (symbol), and apparently $value4 is undefined. The reason it is undefined is because you assign it the value of $_[4] but you probably want $_[3] (since arrays are zero-indexed.)

It looks like you intend $value4 to be a file name for your output; if that's the case then you need to actually open that file to get a filehandle:

open my $fh, '>', $value4 or die "Could not open file $value4: $!";
...
print { $fh } $k." = ".%{$value2{$k}}. $value3;

So you have three things to fix:

1. Figure out why $value4 is undefined and fix that. (When you find yourself appending numbers onto the names of scalars, chances are you probably want to use an array anyway. You could use just @_ directly or grab the values into an @args array rather than a bunch of scalars.)

2. Figure out how you want to format your output string and use a filehandle, not a filename, for print.

3. Figure out how you want to serialize the hash referenced by $value2{$k}, because printing a hash in scalar context is almost certainly not what you want to do.

(Updated suggestions after I realized you're lacking a filehandle)

来源：https://stackoverflow.com/questions/16391047/cant-use-an-undefined-value-as-a-symbol-perl